1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and a manufacturing method thereof.
2. Description of the Background Art
In accordance with recent trend in increasing the frequency of electronic equipment such as personal computers, instantaneous supply of current to electronic circuits is required. For this reason, it is desired to develop solid electrolytic capacitors having a smaller value of equivalent serial resistance (hereinafter referred to as ESR).
It is noted here that the ESR is the sum of dielectric loss, resistivity of an electrolyte, and contact resistance between the electrolyte and a cathode. In a high frequency region, the resistivity of an electrolyte and the contact resistance between the electrolyte and a cathode are predominant.
In general, solid electrolytic capacitors have been in use in which a cathode layer is formed by adhesion of a conductive material, such as manganese dioxide, on the surface of a dielectric layer formed by oxidization of an anode composed of the above-mentioned metal.
Because of the low conductivity of manganese dioxide, however, solid electrolytic capacitors using conductive polymers, such as polypyrrole or polythiophene as electrolytes have been developed (refer to, for example, JP-63-173313-A.)
As mentioned above, the ESR of a solid electrolytic capacitor is mostly dependent upon the resistivity of an electrolyte. However, the conductivities of the above-mentioned conductive polymer materials, such as polypyrrole or polythiophen used as electrolytes are almost equal to those of semiconductors, which are lower than the conductivities of metals by approximately three orders. The conductivity of polypyrrole, for example, is 10 to 102 S/cm−1. For this reason, it has been difficult to reduce the ESR in a high frequency region.